1. Field of the Invention
The present invention relates to a conveying apparatus, printing apparatus, control method, and sheet feeding method.
2. Description of the Related Art
A printing apparatus which prints images on a roll-like sheet such as roll paper has been proposed. A printing apparatus like this includes a conveying mechanism which pulls out a sheet from a roll and conveys the sheet. The conveying mechanism includes, for example, a pair of conveyance rollers which clamp and convey the sheet. The sheet conveyance accuracy of the conveying mechanism has influence on the quality of a printed image. The tension of the sheet between the roll and conveyance roller pair has influence on the conveyance accuracy. When the roll is exchanged or the sheet is consumed, the roll diameter changes, and this fluctuates the tension of the sheet. Japanese Patent Laid-Open No. 2009-208921 has disclosed an apparatus which adjusts the tension of the sheet by a spindle motor for driving a spindle which supports the roll. This apparatus disclosed in Japanese Patent Laid-Open No. 2009-208921 executes a process of estimating the roll diameter whenever a printing execution instruction is issued or when a user's instruction is input, and controls the spindle motor based on the estimated roll diameter, thereby suppressing the fluctuation in tension of the printing medium.
The sheet tension can also fluctuate due to a cause other than the roll exchange or sheet consumption. For example, an error of the mechanism of the apparatus or the eccentricity of the rotation center of the roll can also be a cause. It is difficult for the apparatus disclosed in Japanese Patent Laid-Open No. 2009-208921 to cope with the fluctuations in tension of the printing medium resulting from these causes.